In the treatment of hearing loss, a variety of devices have been developed and used to augment the volume of or focus sound entering the sufferer's ear(s). For example, physical devices such as the ear trumpet have a narrow end for insertion into the ear canal and expands steadily out to a flared or bell end. Sound collected by the larger, flared end is directed through to the narrow end to be focused on the individual's ear drum. The trumpet can be maneuvered to some degree within the ear so that the flared end is generally pointing toward a sound of interest (e.g. a person speaking). While such focusing of sound provides a better opportunity to hear, there is no amplification of the sound volume, and of course the size of the device and the need to hold it to one's ear may make it undesirable.
Smaller, electronic personal hearing aids have been developed, many of which can be hidden behind the wearer's ear. In general, such devices acquire sound arriving at the user's ear, convert it to an electronic signal and amplify it, and send the electronic signal to a speaker in or adjacent the wearer's ear. In that way, the volume of the initial sound acquired by the hearing aid is increased, allowing the wearer's diminished hearing to receive and/or understand the sound. However, such devices also amplify background noise that is necessarily present along with conversation or other sounds the wearer desires to hear. Further, such hearing aids (having both a microphone for picking up sound and a speaker for delivering it to the wearer) can on occasion feed back, creating an unpleasant squeal. The electronic parts of such hearing aids can also be negatively affected by external devices or interference.
Systems have been developed to assist hearing using FM-based broadcasting. For example, a microphone is worn by a public speaker or other presenter, and the sound of the presenter's voice into the microphone is transmitted over an FM frequency to a fixed central receiving unit (e.g. sound board). That receiving unit then retransmits the sound over another frequency to be picked up by a radio-type receiver box, and a headphone or in-ear speaker is plugged into that receiver box, as though it were a personal music player. The size and complexity of available equipment renders such systems impossible for the user to take along with him or her. Such systems are designed for large areas such as auditoriums, theaters or churches, and for accommodating a number of users at a time. In that context, FM broadcast to and from a central receiving unit is practical and at reasonable cost.
Nonetheless, problems exist with such systems. As already indicated, such systems are built for a particular room or venue, not for continuous portable use by a particular user. The user cannot carry along the equipment used for such systems, and such equipment is generally too expensive for purchase and use by individuals in a population. Use of FM transmission also can suffer from interference from other transmissions or from electronic devices in the area. Further, it has been observed that re-transmission of FM signals as a part of a hearing-assist device can introduce an appreciable time-lag or lack of synchronization with the user's observation of the speaker or other source of sound. While some users may find that lag tolerable, it is nonetheless generally undesirable.